When And Why Can Chemicals Be Harmful?

Lucy Bell-Young

by Lucy Bell-Young

3rd March 2021

Many everyday products that we use are in fact chemicals, from the baking soda in our kitchen cabinets and the detergents under our sinks, to drain cleaners, air fresheners and yes, your food additives as well. This can cause alarm for many people because the word ‘chemical’ has come to sound dangerous and toxic – but not all chemicals are harmful. 

Chemicals are only considered harmful in the context of the danger or threat that they can pose to the normal cycle of biochemical reactions, i.e. metabolic and bioelectrical processes. When certain chemicals interrupt, inhibit, redirect, or totally halt these normal biochemical reactions, they can be toxic, venomous, corrosive, flammable or carcinogenic. 

This article explores the six categories of harmful chemicals, what harmful chemicals are, and whether all chemicals are dangerous to humans. 

Concept of dangerous, harmful or toxic chemical substance

Are All Chemicals Harmful?

Not all chemicals are harmful because many chemicals, like water, vitamins, minerals, amino acids, and oxygen, are essential to life. Life as we know it simply wouldn’t be possible without chemicals and chemical reactions. In fact, approximately 37×1012 (or 37 thousand billion billion) chemical reactions occur in the human body every second.

The most widely held belief about chemicals is that they’re bad, with images of toxic household chemicals springing to mind, such as hydrochloric acid, bleach, drain unblocker, and paint thinner. It’s true that we encounter hundreds of thousands of chemicals every day, so how can we figure out which chemicals might pose us harm? 

Well, aside from good old common sense (take your medicine but don’t drink the bleach), it helps to be aware of the six categories that harmful chemicals are classified by:

  1. Highly fluorinated chemicals

Highly fluorinated chemicals are present in various products that are designed to be water-resistant and non-stick. Common products that contain these chemicals are non-stick cookware, carpeting, outdoor apparel, and food packaging. Examples of highly fluorinated chemicals include perfluoroalkyl chemicals (PFAS).

These chemicals are among the most persistent environmental pollutants across the globe and are linked to a wide range of chronic and acute diseases, such as kidney cancer, testicular cancer, elevated levels of cholesterol, and morbid obesity.

  1. Antimicrobials

Antimicrobials are chemicals designed to kill or inhibit the population growth of microbes on surfaces. Thus, they can kill harmful microbes, particularly pathogenic bacteria. This group of chemicals includes triclosan and triclocarban, which are common ingredients in many hygiene products like soap, deodorant, and toothpaste. They can also be found in brand new socks, lunch boxes, and kitchen countertops as protection against bacterial growth.

Unlike antibiotics, antimicrobials are not meant to be ingested. When ingested or absorbed through the skin, they can disrupt the normal functions of the endocrine, thyroid, and the reproductive systems. They may also cause the development of superbugs or strains that are highly resistant to antibiotics.

  1. Flame retardants

Some household items that typically contain flame retardants are furniture, baby product foam, electronic appliances or gadgets, and building insulation. While these chemicals are resistant to fire, they can also be very toxic. Flame retardant chemicals include phosphorus, bromine, chlorine, nitrogen, and even some metals.

These chemicals are usually associated with problems with the endocrine glands and reproductive system. They can also adversely affect the immune system and the nervous system. In some cases, flame retardants have even been linked to cancer.

  1. Bisphenols and phthalates

Bisphenols and phthalates are chemicals found in plastics, pesticides, and flame retardants. Bisphenol-A, more commonly known as BPA, is the most notorious chemical in this group. It’s also the most common, being used in the linings of bottles and soda cans, though its concentration here is too low to cause any adverse effects. 

In general, though, bisphenols and phthalates are toxic when ingested or inhaled as vapours because they behave as endocrine disruptors. This means that they’re able to disrupt the normal hormone signaling mechanisms in the human body. Even at small concentrations, these chemicals can affect the reproductive and immune systems, causing developmental problems in the foetus. They can also affect the neurologic system, resulting in various neurological problems, such as tremors. 

  1. Organic solvents

Organic solvents refers to hydrocarbons, ketones, and glycol ethers that are used as thinners for paint and coatings. They’re also used as degreasers and chemical cleaners. Some examples are:

As solvents, these organic compounds can dissolve other polar organic compounds. Virtually all of these chemicals have noxious vapours which, when inhaled and absorbed into the lungs, can cause nausea and vomiting. Some of them also have carcinogenic properties, with research showing that short-term, high level exposures to these chemicals and long-term, low-level exposures are both associated with various types of cancers. They can also adversely affect the reproductive system.

  1. Heavy metals

Elemental metals like lead, zinc, aluminium, mercury, and cadmium are found in trace amounts in the environment. They’re also commonly found in some of the products that we use in everyday life, like batteries and thermometers.

If chronically ingested, these metals can accumulate in the cells and cause organ damage. They can also damage the central nervous system, lungs, kidneys, and liver. Another harmful side effect of heavy metals is abnormal blood clotting: one study indicates that mercury can cause abnormal blood coagulation and thrombin generation. 

Many of colorful chemicals on Erlenmeyer flask with Variety type of chemical hazard warning symbols labels on
Always make sure you check the safety labels on any chemical product you use

How Do Chemicals Cause Harm?

Certain chemicals can cause harm to the environment as well as to biological organisms, including humans, if the following conditions are true:

  • The chemicals are present or consumed in excessive amounts 
  • They don’t naturally belong in a particular ecosystem, such as the presence of oil spills in the ocean
  • They disrupt normal biological functions or have carcinogenic properties
  • They are highly corrosive, which could dissolve organic tissue like skin
  • The chemicals are radioactive and emit high levels of ionising energy
  • They react with other chemicals, forming toxic substances
  • They are potentially explosive under pressure or high heat

What Are Harmful Chemical Reactions?

There are several types of hazardous chemical reactions that are considered harmful because they can disrupt or destroy normal biological functions, or cause ecological imbalances and environmental destruction.

Here are some examples of harmful chemical reactions:

  • Corrosive reactions from acids and alkalis
  • Explosive reactions or sudden combustions, such as LPG explosions
  • Oxidising reactions, such as ozone reactions with organic tissues
  • Bleach reactions, which can harm the skin
  • Toxic gas generation from other chemical reactions, such as organic decomposition

Are All Chemicals Harmful To Humans?

Obviously, not all chemicals or chemical reactions are harmful to humans. While there are several household chemicals that are harmful when ingested, inhaled or when they come into contact with the skin, these risks are usually very easy to safeguard against. 

Many chemicals, like the food we eat, the water we drink and the medicines or vitamins we take, are absolutely necessary to our survival. Similarly, there are some chemicals that have the potential to be harmful but are also important to everyday life, like antifreeze, hydrogen peroxide, and pesticides. 

When we navigate around so many chemicals day-to-day, it becomes almost impossible to completely limit your exposure to harmful chemicals. The best thing you can do to protect yourself is to always read the safety labels on whatever product you’re using, as well as the guidelines on storage and directions of use.


All content published on the ReAgent.ie blog is for information only. The blog, its authors, and affiliates cannot be held responsible for any accident, injury or damage caused in part or directly from using the information provided. Additionally, we do not recommend using any chemical without reading the Material Safety Data Sheet (MSDS), which can be obtained from the manufacturer. You should also follow any safety advice and precautions listed on the product label. If you have health and safety related questions, visit HSE.gov.uk.